Thurrell, Adrian Edward Ivan; (2004) Multisensory interactions concerning human self-motion. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Humans move in their environment and have a number of different sources of information about their self-motion, e.g. visual, vestibular, proprioceptive and somatosensory signals. These signal sources must be combined to overcome their individual limitations. As the eyes are mobile relative to the trunk, gaze direction must be taken into account if visual information is to be applied usefully to control posture. The orientation of the postural response to visual motion in various directions relative to the subject is investigated using two paradigms. In the first, using passive motion of the subject in a dark room, it is difficult for subjects to cognitively reconstruct the direction of gaze, and hence, the visual motion. The data show that the postural response may take account of the gaze direction independently of cognitively mediated knowledge of the geometry of the experimental conditions. In the second, comparisons are made between the accuracy of this reorientation during the visually induced perception of self-motion (vection) and object-motion perception and it is found that the accuracy of the reorientation is improved during conscious perception of self-motion (vection). During locomotion, visual signals corresponding to object motion are distorted by motion components directly related to the speed and direction of movement by the observer. Thus, in order to allow a veridical interpretation of the visual signal by the observer, these self-motion components must be discounted, while at the same time retaining important information on their speed and progression. In experiments, the effects of proprioceptive, somatosensory and efference copy signals of self-motion are isolated by comparing the speed of a constant optic flow stimulus that is perceived while either standing or performing a motor activity. It is found, firstly, that the more locomotion-related a motor activity may be, the greater it reduces the perceived speed. And secondly, that the more locomotion-related a visual stimulus is, the greater its perceived speed is reduced while walking. It is therefore suggested that a tuning exists between locomotor activity and the types of visual signal (i.e. optic flow) that it normally introduces. The above experiments suggest a network of self-motion signals that are combined dynamically to represent the movement of the body. This single representation is used both to control self-motion and to compensate for its effects on visual processes.

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